The Value of a Pet Scan in Selecting the Best Lymph Node to Biopsy, and Confirming the Diagnosis of Idiopathic Multicentric Castleman Disease with HLH And EBV Viremia in a Previously Healthy Adult

Introduction
Castleman disease (CD) is a rare lymphoproliferative disorder with diverse clinical presentations. The idiopathic HIV- and HHV8-negative multicentric subtype (iMCD) poses a significant diagnostic challenge due to its non-specific manifestations. iMCD typically presents as diffuse lymphadenopathy accompanied by systemic inflammatory symptoms driven primarily by interleukin-6 (IL-6). Treatment strategies focus on reducing inflammation through IL-6-targeted monoclonal antibodies, such as siltuximab, and in severe cases, utilizing immuno-chemotherapy to manage B- and plasma-cell activation.
Case Description
A 43-year-old previously healthy man presented to the emergency department with fever, night sweats, anasarca, anemia, thrombocytopenia, and acute renal insufficiency. Comprehensive blood tests and imaging were performed, with initial considerations including viral infections (such as COVID-19), hemophagocytic lymphohistiocytosis, lymphoma, and autoimmune diseases. An initial axillary lymph node biopsy was inconclusive. A positron emission tomography (PET) scan revealed diffuse, symmetrical lymphadenopathy involving the cervical and hilar/mediastinal regions. Subsequent mediastinal lymph node biopsy confirmed a diagnosis of iMCD. The patient was treated with high-dose corticosteroids and siltuximab. Epstein-Barr virus (EBV) PCR returned positive, prompting the addition of rituximab to APX-115 the regimen. The patient experienced full recovery and reported well-being within two months.
Conclusions
The diagnosis of iMCD was complicated by its non-specific symptoms, an inconclusive initial biopsy, and overlap with hemophagocytic lymphohistiocytosis. PET imaging proved essential in selecting the most suitable lymph node for biopsy. While anti-IL-6 therapy remains the cornerstone of treatment, questions persist regarding the optimal duration of siltuximab therapy, long-term toxicity, and its immunosuppressive effects. Additionally, the role of EBV reactivation in the pathogenesis and management of iMCD warrants further investigation.
Learning Points
• PET imaging is a critical tool for identifying the optimal lymph node biopsy site in suspected iMCD cases.
• Epstein-Barr virus reactivation may contribute to the pathogenesis of iMCD and influence treatment strategies.